The emigration of Irish people to America began in colonial times and reached its highest point in the Great Famine of the 1800s. Early Irish immigrants were predominantly Scotch-Irish from Ulster and Northern Ireland. There were not many Irish Catholics in America until about 1800, but after that they started to immigrate in large numbers as they fled British oppression and the resulting famines. In the United States, which was predominantly Protestant at the time, the Irish were the first major Catholic presence and because of that they were subject to virulent discrimination. Immigrants from Ireland, most of whom were illiterate farmers, congregated in the big industrial centers of the Northeast, Middle Atlantic and Midwest regions of America. They lived in overcrowded housing and worked whatever jobs they could find, preferring to starve there than to return to growing crops.
The proportion of the Irish population that fled to the United States was higher than that of any other country. However, the influx of Irish people in America slowed significantly at the beginning of the twentieth century and it virtually ceased after Ireland was declared independent in 1921. After that, Irish continued to move to the United States in small numbers, but the mass migration had come to an end. Americans discriminated and treated Irish badly not only because of their religion, but also because they believed their jobs were under threat due to the influx of workers willing to be paid extremely low wages. However, Irish Americans helped fill the need for workers when the extensive constriction of canals, railroads, bridges and the expansion of the country's mining industry began in the middle and late nineteenth century. Much of the railroad track across the country was also laid by Irish Americans, so without their labor the US development would have been much slower. Irish Americans' participation in the armed services also helped improve their image in the United States.
Later, when there were waves of immigrants from Eastern Europe, Irish Americans seemed much more "American" and started to be welcomed into the mainstream society. The Irish American community was also becoming better known in politics. Their success in political maneuvers led to a dramatic improvement of their situation in America. Irish Americans also participated actively in the labor movement between the 1870s and the 1930s. While in early history Irish immigrants were concentrated in certain areas of the United States, later they were spread relatively evenly throughout the entire country. The states with the highest proportion of Irish Americans are Massachusetts, New Hampshire, Rhode Island, Connecticut, Delaware, Vermont and Pennsylvania.
Irish American's most obvious contribution to American culture is St. Patrick's Day, which is observed on 17 March. The Catholic Church in America also still tends to be defined through Irish Catholicism. Among the best-known Irish Americans who have contributed significantly to American culture are composers George M. Cohan and Victor Herbert, along with musicians Jim Morrison, Mariah Carey and Alicia Keys. Irish American actors include Ben and Casey Affleck, Grace Kelly, Patrick Duffy, Jack Nicholson, and Lindsay Lohan. Georgia O'Keeffe is the best-known Irish American artist, while architect Louis H. Sullivan, who developed the skyscraper design, was also Irish American.
Irish American Eugene O'Neill is the only American playwright ever awarded the Nobel Prize. Other Irish American writers include John O'Hara, F. Scott Fitzgerald, Mary Higgins, Kate Chopin (born Katherine O'Flaherty), William Kennedy, Andrew Greeley, Mary Gordon and poets Franc O'Hara, Galway Kinnell and James Whitcomb Riley. Irish American leaders in industry, science and politics include the Kennedy Family, former Chicago mayor Richard Daley and his son, also elected mayor of Chicago, Richard M. Daley. Sandra Day O'Connor was the first woman to be appointed justice of the Supreme Court, while astronaut Kathryn Sullivan was the first woman to walk in space. Henry Ford, who built the first inexpensive automobile, the Model T, was also Irish American, as was the winner of the Nobel Prize for Economics in 1981, James Tobin.
Noteworthy journalists and other media personalities of Irish descent are Norah and Kelly O'Donnell, Conan O'Brian and Chris Matthews. Famous Irish Americans in sports include boxers Paddy Ryan, John L. Sullivan, Jack Dempsey and Gene Tunney, as well as baseball player pitcher Nolan Ryan and shortstop Derek Jeter. Two notorious Irish Americans were outlaw Billy the Kid, born Henry McCarty and Senator Joseph R. McCarthy, who instigated the American anti-Communist hysteria of the 1950s, later known as "McCarthyism".